Extended Data Fig. 5: A570D-associated inter-protomer interactions within S-UK.

The expanded views of the reported S-UK structures superimposed with the current study. Top panels. S-UK structures in the RBD-up state. The S-UK structure reported in this study is colored in tomato. Bottom panels. S-UK structures in the RBD-down state. The S-UK structure reported in this study is colored in orchid. The S-UK structures reported by Cai et al.¹ (PDB entry 7N1Y) and Gobeil et al.² (PDB entry 7LWV) are shown in semitransparent gray and magenta, respectively. The corresponding protomer chain IDs are indicated in subscripts. In the RBD-up state, Cai et al. observed the same inter-protomer salt bridge between A570D and K854 while the corresponding K854 is missing in the atomic model reported by Gobeil et al. In the RBD-down state, both Cai et al. and Gobeil et al. reported an inter-protomer hydrogen bond between A570D and N856 whereas we observed an inter-protomer salt bridge between A570D and K964 from the other protomer opposite of the other studies’ findings. The inter-protomer salt bridges and hydrogen bonds are indicated by black dashed lines.